Project Summary It is well established that physiologic, imaging, and circulating biomarkers of right ventricular (RV) dysfunction predict adverse outcomes in pulmonary arterial hypertension (PAH), yet our understanding of the genetic, molecular, and cellular determinants of RV failure is nascent. Further, there is a clear clinical need to identify targets directed at preserving and improving RV function in PAH. In this context, our global objectives are to identify and characterize novel molecular determinants and clinical biomarkers of RV function and failure and define both their contribution to disease phenotype and their potential for exploitation as therapeutic targets. Recognizing that cardiopulmonary dysfunction in PAH is linked to pathologic changes in the microvasculature, we rationalized that circulating antagonists of microvascular homeostasis could negatively impact on disease pathogenesis. We have demonstrated that endostatin (ES), a potent inhibitor of angiogenesis (i.e., angiostatic factor), is elevated in PAH, associated with adverse hemodynamic and functional status, and, importantly, w i t h increased mortality in idiopathic and connective tissue disease associated PAH (IPAH and CTD-PAH, respectively). Further, we have identified multiple genetic variants in the gene encoding ES (Col18a1) that are associated with potential altered protein function, protein expression, cardiac function, and outcomes in PAH. This is a five-year grant proposal put forth jointly by a new and an established investigator on the role of Col18a1 / ES on PAH. The objectives of the grant are to further define the relationship between ES and cardiopulmonary structure and function in disease, to further define and characterize the molecular and cellular effects of variants in the gene encoding ES (Col18a), and to provide necessary preclinical data on the impact of ES antagonism as a potential therapeutic target in PAH.